The truck's occupant and three firefighters were taken to a hospital, the newspaper said. A fifth person drove himself to the hospital. Briggs School was closed, Highway 126 was shut down, people within a mile of the site were evacuated, and those within three miles of the explosion were told to shelter in place.

Capt. Mike Lindberry of the Ventura County Fire Department told the station that the chemical is water reactive, meaning that attempts to extinguish the fire with water could accelerate the chemical reaction.

"Right now, we are letting the areas on fire burn down," he said.

The Los Angeles County Fire Department is assisting the Ventura County Fire Department, according to a Twitter post.